Hydrocarbons such as crude and other oils are frequently transported by pipelines. These pipelines are thousands of miles in total length and as a delivery infrastructure are aging in the United States. With this aging comes the need to inspect a pipeline to determine its integrity and maintain the pipeline assets with lowest possible cost.
Amongst the methods for inspecting pipelines are those used for detecting leaks in the pipeline. These range from manual inspection using trained dogs to advanced satellite based hyper spectral imaging. The various methods can be classified into non-optical and optical methods, or external (direct) and internal (inferential). The primary non-optical methods include acoustic monitoring, gas sampling, soil monitoring, flow monitoring and software based dynamic modeling.
Optical methods for leak detection can be classified as either passive or active. Active methods illuminate the area above the pipeline with a laser or a broadband source. The absorption or scattering caused by natural gas molecules above the surface is monitored using an array of sensors at specific wavelengths. If there is a significant absorption or scattering above a pipeline, then a leak is presumed to exist. The basic techniques for active monitoring include Tunable Diode Laser Absorption Spectroscopy (TDLAS), Laser Induced Fluorescence (LIF), Coherent Anti-Raman Spectroscopy (CARS), Fourier Transform Infrared Spectroscopy (FTIR) and evanescent sensing.
Passive monitoring of hydrocarbon leaks is similar to active monitoring in many aspects. However, the major difference between active and passive techniques is that passive techniques do not require a source. This makes passive systems less expensive. However, since a strong radiation source is not employed, many more expansive detectors and imagers have to be used with the passive systems. Two major types of passive systems used for monitoring leaks from hydrocarbon pipelines are thermal imaging and multi-wavelength imaging.
The method of leak detection selected for a pipeline is dependent on a variety of factors including pipeline characteristics, product characteristics, instrumentation and communications capabilities and economics.
Pipeline systems vary widely in their physical characteristics and operation functions and no one external or internal method is universally applicable or possesses all the features and functionality required for perfect leak detection performance.
The present invention provides for improved leak detection methods in hydrocarbon pipelines.